1. Field of the Invention
The invention relates in general to coordinate measurement machines (CMMs) and in particular to portable CMM's having an articulated arm with a rotatable handle.
2. Prior Art
Currently, portable articulated arms are provided as a measurement system with a host computer and applications software. The articulated arm is commonly used to measure points on an object and these measured points are compared to computer-aided design (CAD) data stored on the host computer to determine if the object is within the CAD specification. In other words, the CAD data is the reference data to which actual measurements made by the articulated arm are compared. The host computer may also contain applications software that guides the operator through the inspection process. For many situations involving complicated applications, this arrangement is appropriate since the user will observe the three-dimensional CAD data on the host computer while responding to complex commands in the applications software.
An example of a prior art portable CMM for use in the above-discussed measurement system is disclosed in U.S. Pat. No. 5,402,582 ('582), which is assigned to the assignee hereof and incorporated herein by reference. The '582 patent discloses a conventional three-dimensional measuring system composed of a manually operated multi-jointed articulated arm having a support base on one end thereof and a measurement probe at the other end. Commonly assigned U.S. Pat. No. 5,611,147 ('147), which is again incorporated herein by reference, discloses a similar CMM having an articulated arm. In this patent, the articulated arm includes a number of important features including an additional rotational axis at the probe end thus providing for an arm with either a two-one-three or a two-two-three joint configuration (the latter case being a 7 axis arm) as well as improved pre-loaded bearing constructions for the bearings in the arm.
Commonly assigned U.S. Pat. No. 5,978,748 ('748), which is incorporated herein by reference, discloses an articulated arm having an on-board controller which stores one or more executable programs and which provides the user with instructions (e.g., inspection procedures) and stores the CAD data that serves as the reference data. In the '748 patent, a controller is mounted to the arm and runs the executable program which directs the user through a process such as an inspection procedure. In such a system, a host computer may be used to generate the executable program.
The prior art devices are limited in that they are capable of measuring only one point in space at a time. Products have become available that replace the single point probe with a line laser scanner and charge-coupled device (CCD) that are capable of simultaneously measuring a locus of points on the surface of an object that lie on a plane defined by a scanning laser. An example of such a prior art product is the ScanWorks™ manufactured by Perceptron of Plymouth, Mich. However, such prior art devices are retrofit onto the existing articulated arms of portable CMM's and require external, high bandwidth data connections from the scanner to the host computer used to interpret the image data generated by the CCD as well as external connections to power supplies. Thus, the electrical lines extend outside the housing of the articulated arm. Furthermore, when the single-point probe is replaced by the line laser scanner retrofit, the highly accurate single point probe functionality is lost or at least diminished.